I think Robert Downey Jr IS the cinematic Tony Stark, the same way that Harrison Ford IS Indiana Jones or Bruce Willis IS John McClane. And to me, getting a new actor to play Stark - be it for a sequel or a reboot - would be like getting a new actor to play Jones or McClane: yes, they COULD do it, and eventually they probably WILL do it, but that doesn't make it any less stupid. It just won't be the same.

Yeah and Jack Nicholson IS The Joker.....oh...wait....****

I love RDJ as Tony, but you can recast ANYBODY for these comic book films because most of these characters have over 40 years worth of history, which leads to 100s of different interpretations of the character. Someone may not be able to be RDJ's Tony, but someone can be a different style Tony that is still true to the source material. Again, look at Jack and Heath. Sure, overall you can tell it is the same character, but both interpreted Joker very differently and both interpretations/performances were extremely well received.

__________________"If you figure a way to live without serving a master, any master, then let the rest of us know, will you? For you'd be the first person in the history of the world."
-LANCASTER DODD